Optical fiber cable chemical stripping fixture

ABSTRACT

An elongated fixture handle member is connected to a fixture body member with both members having interconnecting longitudinal central axial bores for the passage of an optical cable therethrough. The axial bore of the fixture body member, however, terminates in a shoulder stop for the outer end of a jacket of the optical cable covering both an optical fiber and a coating therefor, with an axial bore of reduced diameter continuing from the shoulder stop forward for a predetermined desired length to the outer end of the fixture body member. A subsequent insertion of the fixture body member including the above optical fiber elements into a chemical stripping solution results in a softening of the exposed external coating thereat which permits easy removal thereof from the optical fiber while leaving a desired length coated fiber intact within the fixture body member.

ORIGIN OF THE INVENTION

The invention described herein was made by employees of the UnitedStates Government, and may be manufactured and used by or for theGovernment for Governmental purposes without the payment of anyroyalties thereon or therefor.

FIELD OF THE INVENTION

This invention relates generally to a method and apparatus for strippingan optical fiber cable and, more particularly, to a method and apparatusfor chemically removing the coating surrounding glass fibers in opticalfiber cables.

BACKGROUND OF THE INVENTION

Heretofore, when the coating needed to be removed from the optical fiberof an optical fiber cable so that it can be terminated with a connectorassembly or terminals, it typically involved using electrical wirestripping techniques or the fiber was simply dipped and withdrawn from achemical stripping solution by hand.

Mechanical fiber coating removal techniques, however, can nick, scratch,score or otherwise damage extremely small and fragile optical fibers.Such damage is difficult to detect and can result in a latent defect inthe cable which is unacceptable in high reliability applications. Handheld chemical removal techniques also do not provide the controlnecessary to strip the fiber coating to precise lengths, and generallydo not produce sharp, well defined edges or interfaces between theoptical fiber and the fiber coating.

SUMMARY

It is an object of the present invention, therefore, to provide animprovement in the removal of coatings from optical fiber.

It is a further object of the invention to improve the chemical removalof coating which surround glass fibers used in optical fiber cables.

It is another object of the invention to provide increasing reliabilityof the chemical removal of optical fiber coatings so that substantiallyflawless optical fiber surfaces are provided.

It is still a further object of the invention to provide fiber coatingremoval of an optical fiber cable to precise dimensions so that thecable can be more efficiently terminated with a connector assembly.

The foregoing and other objects of the invention are provided by anelongated fixture handle member connected to a fixture body member, bothmembers having interconnecting longitudinal central axial bores for thepassage of an optical cable therethrough, the axial bore of the fixturebody member, however, terminates in a shoulder stop for the outer end ofthe inner jacket of the optical cable covering both an optical fiber anda coating therefor, with an axial bore of reduced diameter continuingfrom the shoulder stop forward for a predetermined desired length to theouter end of the fixture body member, whereby a subsequent insertion ofthe fixture body member into a chemical stripping solution results in asoftening of the exposed external coating thereat which permits easyremoval thereof from the optical fiber while leaving a desired length ofcoated fiber within the fixture body member intact.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the invention will be more readilyunderstood when considered in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a side elevational view of an end section of an optical fibercable ready for chemical stripping of the fiber coating from the end ofan optical fiber;

FIG. 2 is an exploded elevational view of three variations of thepreferred embodiment of the subject invention;

FIG. 3 is a central longitudinal cross sectional view of one fixturebody shown in FIG. 2 attached to a fixture handle member; and

FIG. 4 is a side elevational view of the optical fiber cable shown inFIG. 1 with a portion of the fiber coating stripped from the opticalfiber.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly to FIG. 1, shownthereat is an end portion of an optical fiber cable 10 which iscomprised of an outer jacket 12 within which there is an intermediatecloth-like member 14 and an inner jacket 16 which in turn covers acoating 18, covering an optical conductive fiber 20, typicallyconsisting of glass. The coating 18 is typically comprised of a wellknown material such as acrylate.

Before the optical fiber cable 10 can be terminated with a connectorassembly or terminals, however, a certain portion of the coating 18 mustbe removed or stripped from the glass fiber 20. Moreover, depending uponthe type of termination required, an exposed length L of fiber coating18 must remain intact, such that it projects from the outer end 22 ofthe inner jacket 16, with the exposed glass fiber 20 then being severedat an appropriate length, leaving a structure such as shown in FIG. 4.

To accomplish this result and where the length L is variable and yetcontrolled so as to have a very precise dimension, a chemical strippingfixture, shown in FIG. 2, comprised of two elements fabricated from aninert material, such as tetrafluoroethylene (TFE), a fixture handlemember 24 and a fixture body member 26, are coupled together with theend of the optical fiber cable 10 to be stripped inserted therein asshown in FIG. 3. The handle member 24 is shown connectable to one ofthree different fixture body members 26-1, 26-2 and 26-3 by beingscrewed together by mating threads 28 and 30, respectively.

As further shown in FIG. 2, the fixture handle member 24 comprises anelongated member which is generally cylindrical in cross section andwhich is typically three inches long and 0.5 inches in diameter. Thehandle member 24 includes an external flat portion 32 for gripping andmarking and a longitudinal central axial bore 34 which includes a flutedouter end 36. The inner end of the axial bore 34 terminates in athreaded inner end portion 38 of relatively larger diameter and whichincludes female type threads 28.

Each of the fixture body member 26-1, 26-2 and 26-3 are substantiallyidentical in construction with the exception that three different borelengths L₁, L₂ and L₃ are implemented by respective central longitudinalaxial bores 40 having a relatively smaller diameter to accommodate aglass fiber 20 and its associated fiber coating 18 (FIG. 1). At theinner end of the bores 40, there is located a relatively larger shoulderportion 42 which is dimensioned to receive the forward end 22 of theinner jacket 16, also shown in FIG. 1. The rear ends of the fixture bodymembers 26-1 . . . 26-3 include a set of male type threads 30 and arelatively larger longitudinal axial bore 44 whose diametersubstantially matches that of the bore 34 in the handle member 24. Thefixture body members 26-1 . . . 26-3 each include an intermediate bodyportion 48 and have a flat gripping and marking surface 50 at the frontthereof. A reduced diameter tip portion 52 extends from the intermediatebody portion 48. The tip portion 52 includes a peripheral notch 54 apredetermined distance back from the end face 56 and acts as animmersion line for the operation now to be explained.

When an optical fiber cable 10 is ready for removal of the fiber coating18, the cable is first inserted into a disassembled stripping fixture,as shown in FIG. 2, comprised of the handle member 24 and one of thefixture body members 26-1, 26-2, 26-3, where it is seated into thefixture body member 26-1, for example, such that the end surface 22(FIG. 1) of the inner jacket 16 abuts the shoulder 42. Once the cable 10is seated properly, the coated optical fiber 20 and the fiber coating 18to be stripped therefrom protrudes from the tip portion 52. The fixturehandle member 24 is screwed onto the fixture body 26-1 and the cableassembly is picked up via the fixture handle member 24. The protrudingfiber 20 and its fiber coating 18 is immersed into an appropriatechemical stripping solution up to the notch 54 encircling the tipportion 52. The immersed fiber elements are held in the strippingsolution until the fiber coating 18 softens, which is typically about 90seconds. At this point, the fiber coating 18 is removed up to the frontend face 56 of the tip portion 52, by sliding the fixture body member26-1 off the cable 10 or by wiping the softened coating 18 off using acloth, leaving a length L of fiber coating 18 within the fixture bodymember which when removed therefrom provides a structure such as shownin FIG. 4.

The fixture body members 26-1, 26-2 and 26-3 ensure that optical fibersare stripped to a precisely controlled lengths L₁, L₂ and L₃,respectively, typically within 0.010 inches and that the remaining fibercoating 18 has a sharp well defined interface 58 as shown in FIG. 4.

The stripping fixture according to the subject invention, when used withchemical stripping solutions, eliminates the possibility of nicking,scratching or otherwise damaging the extremely fragile optical fibersduring fiber coating stripping operations. The fixture body membertogether with the chemical stripping agent reduces the possibility oflatent defects in the cable in high reliability applications. Both thehandle member and the fixture body member are fabricated from inertmaterials so that the fixture assembly is not damaged or affected bycontact with most chemical stripping solutions used to remove opticalfiber coatings.

Having thus shown and described what is at present considered to be thepreferred embodiment of the invention, it should be noted that the samehas been made by way of illustration and not limitations. Accordingly,all modifications, alterations and changes coming within the spirit andscope of the invention as set forth in the appended claims are hereinmeant to be included.

We claim:
 1. A method of chemically stripping a portion of a coatingcovering an optical fiber of an optical fiber cable, including at leastone outer jacket, comprising the steps of:exposing a first length ofoptical fiber including a coating from an end of said at least one outerjacket; inserting the exposed said first length of said optical fiberincluding said coating into a fixture including a chemically inertfixture body member having a longitudinal axial bore therein, said borehaving a second length and terminating inwardly at a shoulder stop ofsaid body member for receiving said end of said outer jacket, said borefurther terminating outwardly at an outer surface of said fixture bodymember, said first length being greater than said second length so thata portion of said optical fiber including said coating extends beyondsaid outer surface of said fixture body member; immersing said portionof said optical fiber including said coating via the fixture body memberinto a coating stripping solution for a time until said coatingextending beyond said outer surface softens, removing said portions ofsaid coated optical fiber from said stripping solution; and strippingthe softened coating from the optical fiber extending beyond said outersurface, whereby a length of exposed coating remains intact adjacent astripped length of optical fiber.
 2. A method according to claim 1 andadditionally including the step of connecting a handle member to saidfixture body member prior to said immersing step, said handle memberincluding a longitudinal axial bore therethrough and having a diameterfor passing the outer jacket of said optical fiber cable.
 3. A methodaccording to claim 1 wherein said coating is comprised of acrylate.
 4. Amethod according to claim 1 wherein said optical fiber includes anotherouter jacket externally of said at least one outer jacket.
 5. A methodaccording to claim 3 wherein said jackets are separated by astrengthening member.